Hydrophobic effect, lipids and membranes

Hydrophobic substances are ___________________ in water due to their inability to interact favorably with water molecules.

insoluble

The _________________ is the phenomenon by which nonpolar molecules aggregate to avoid contact with hydrophilic molecules, particularly water

hydrophobic effect

After nonpolar molecule aggregation, _________________ become possible.

van der Waals forces (London dispersion)

Hydrophilic substances (polar or charged molecules) dissolve in water because they can form______________________ with water.

hydrogen bonds or electrostatic interactions

The hydrophobic effect causes nonpolar molecules to __________________ in water, reducing their contact with water and thus increasing ________________

aggregate, water's entropy.

When nonpolar molecules aggregate, this organized "cage" of water is disrupted, freeing the water molecules and increasing their ___________________, which is thermodynamically favorable.

entropy

Amphiphilic substances have both hydrophobic and hydrophilic regions. In water, they tend to form structures like __________________. The hydrophilic heads interact with water, while the hydrophobic tails are shielded from water by aggregating together.

micelles or lipid bilayers

Components of a micelle

- Polar head group

- Nonpolar tail (one-tailed)

Depending on the relative sizes of the hydrophilic and hydrophobic portions of the amphiphiles, the molecules may form a _______________ rather than a spherical micelle.

lipid bilayer

components of a lipid bilayer

- Polar head group

- Nonpolar tails (two-tailed)

The hydrophobic core of a lipid bilayer prevents ______________ from easily passing through.

- polar molecules

- ions

- hydrophilic substances

A lipid bilayer tends to close up to form a _________________

vesicle (or liposome)

Only __________________________ can diffuse across the lipid bilayer without assistance, while others require transport proteins or channels.

- small nonpolar molecules

- lipophilic (hydrophobic) substances

Passive diffusion

movement from high to low concentration gradient

Lipids are diverse in structure, and typically characterized by their hydrophobic nature. They are composed of long hydrocarbon chains or rings and can be __________________

saturated (no double bonds) or unsaturated (with one or more double bonds).

__________________ lipids have both hydrophilic and hydrophobic regions.

Amphipathic

Fatty acids can be esterified with _________________ to form __________________

glycerol, triglycerides (fats).

Each hydroxyl group of glycerol forms an _______________ with the _______________ of a fatty acid. This process generates larger structures like triacylglycerols (energy storage molecules) or phospholipids (components of membranes).

ester bond, carboxyl group

Each hydroxyl group of glycerol forms an ester bond with the carboxyl group of a fatty acid. This process generates larger structures like

- triacylglycerols (energy storage molecules)

- phospholipids (components of membranes).

Amphipathic lipids have both hydrophobic (nonpolar) and hydrophilic (polar) regions. For example, phospholipids have a hydrophilic phosphate head and two hydrophobic fatty acid tails. These structures are essential for forming ________________ in cell membranes.

lipid bilayers

Lipids serve various functions and can form:

- Cholesterol

- Fat-soluble vitamins

- Triglycerides

- Phospholipids

Cholesterol modulates membrane fluidity and serves as a precursor for ___________________

steroid hormones

Lipid (fat)-soluble vitamins made from lipids include:

- Vitamin D (sunshine vitamin)

- Vitamin E (alpha-tocopherol)

- Vitamin A (retinol)

- Vitamin K (phylloquinone)

What are Vitamins D,E,A,K good for?

Vit D: Calcium absorption, muscle health

Vit E: Skin, antioxidant

Vit A: vision

Vit K: Clotting

Triglycerides act as ________________ storage molecules.

energy

Phospholipids form the structural basis of ___________________..

cell membranes

The lipid bilayer consists of two layers of phospholipids, with the hydrophobic tails facing inward and the hydrophilic heads facing outward. This structure is semi-permeable, flexible, and provides a barrier to the diffusion of most ______________

polar molecules and ions.

Membrane lipids exhibit two primary types of movement:

- Lateral diffusion

- Transverse diffusion (flip-flop)

Lateral diffusion

Lipids move side to side within bilayer leaflets rapidly

Transverse diffusion (flip-flop):

Lipids move between the inner and outer bilayer leaflets slowly. Often requires enzymes like translocases, flippases, and floppases.

The fluidity of the lipid bilayer depends on its lipid composition:

Saturated fats ___________________ because they can pack tightly together.

increase membrane rigidity

Unsaturated fats ____________________ because the kinked structure of double bonds prevents tight packing.

increase fluidity/mobility

Cholesterol ____________________ restricts movement, and decreases fluidity.

increases membrane rigidity

________________ is common and rapid, allowing lipids to move within the same side of the bilayer.

Lateral diffusion

_________________ is much slower and less frequent because it requires the hydrophilic head to pass through the hydrophobic core, making it energetically unfavorable without the assistance of enzymes like flippases.

Transverse diffusion (flip-flop)

Cholesterol and vitamins are constructed from 5-carbon units, terming them____________

isoprenoids

Cholesterol and vitamins cannot be synthesized, and are obtained from

food